Method of and means for controlling low temperature refrigerants



W. F. BAIRD Aug. 8, 1933.

METHOD OF AND MEANS FOR CONTROLLING LOW TEMPERATURE REFRIGERANTS FiledJuly 13, 1929 Patented Aug. 8, 1933 METHOD OF AND TROLLIN G LOWFRIGERANTS William F. Baird,

MEANS FOR CON- TEMPERATURE RE- Winchester, Mass.

Application July 13, 1929. Serial No. 378,014

6 Claims.

This invention relates to a method of and means for maintaining asubstantially constant temperature in a refrigerator cabinet byautomatically controlling the refrigerating effectof low temperaturerefrigerants such as solid car- 0 the refrigerant changes state.

bon dioxide. The use of solid carbon dioxide as a refrigerating agenthas come into considerable favor due to the ease of handling and theabsence of resultant liquid to be disposed of when There are, however,certain pra etical difliculties connected with the use of lowtemperature refrigerants such as solid carbon dioxide. The refrigeratingeffect of a block of solid carbon dioxide placed within a refrigeratorcabinet is roughly proportional to its free surface, this effect beingvaried by different conditions such as the freedom of circulation ofatmosphere and the conductivity of the support on which the block rests.Thus when a. block of solid carbon dioxide is placed within arefrigerator cabinet upon a shelf or within the cabinet, therefrigerating effect is usually too great while the block is large,causing unnecessary and undesirably low temperatures within therefrigerator. These low temperatures are detrimental to many foodstuffswhich require moderately low temperatures. Furthermore the excessivelylow temperatures in a refrigerator are wasteful in that anunneecessarily steep temperature gradient is established through thewalls of the refrigerator which induces a larger inflow of heat with aresultant wasteful consumption of the refrigerant. When the block ofrefrigerant shrinks to small sire it reaches a point where its size isinsuificient to maintain the refrigerator at a temperature which issufficiently low. Unless the block is then broken up so as to exposemore surface, or more refrigerant is supplied to the refrigerator, thetemperature within the cabinet rises beyond the desired maximum.

It is an object of this invention to provide apparatus for socontrolling the refrigerating effect of carbon dioxide or other very lowtemperature refrigerants that the initial wastefully rapid consumptionof refrigerant is avoided and the last of the block of refrigerant isutilized to maintain a substantially constant temperature within therefrigerator cabinet within a desired temperature range, this regulationof refrigerating effect being automatically self-controlling so as torequire no attention on the part of the operator.

In any refrigerating system wherein a cabinet is cooled by arefrigerating substance, there is a upon goods temperature gradient fromthe atmospheric temperature to the temperature of the refrigerant. Ifthe refrigerator cabinet is properly insulated as it should be, there isa sharp temperature drop between its outer surface and its innersurface, the inner temperature being preferably at or near that desiredfor the foodstuffs or other objects which are to be kept cool within thecabinet. For example, a cabinet for fresh meats should be maintained atabout F. while for ice cream a temperature of 5 to 8 F. is de sirable.Where solid carbon dioxide is used as a refrigerant, there isnecessarily a large temperature difference between the interior. of therefrigerator cabinet and the refrigerant itself owing to the fact thatthe latter is approximate- 1y 118 below zero F.

It is a further object of this invention to provide self-regulatingapparatus which will automatically vary the heat conductivity of thepath between the interior of the refrigerator cabinet and therefrigerant, so that the heat flow along that path shall balance theinflow of heat through the walls of the cabinet, the apparatusautomatically adjusting itself to take care also of occasional inflow ofheat resulting from the opening of the cabinet doors for the insertionor removal of merchandise. It is desirable that the control apparatus benot only capable of adjusting itself automatically to regulate the flowof heat from the refrigerator cabinet to the refrigerant so as to equalthe inflow through the walls of the cabinet, but also to respond quicklyto .a change of inflow so that when the cabinet temperature is raised bythe opening of the doors the refrigerating apparatus quickly absorbs theextra heat and restores the cabinet temperature to its desired value.

It is a still further objectof the invention to provide apparatus suchthat if desired the refrigerant may be somewhat remote from the cabinet.This affords considerable freedom in designing refrigerating apparatus,since it is not necessary that the refrigerant be within or immediatelyadjacent to the cabinet.

In carrying out the present invention so as to .provide one form ofapparatus having the desirable characteristics hereinbefore mentioned, Imay provide a receptacle for the solid carbon dioxide such that aportion of its surface can be maintained at a temperature approximatelyequal to that of the refrigerant itself. To this end the receptacle ispreferably made of metal and may be provided with a number of finsextending upwardly from its bottom, these fins being adapted to supportthe block of carbon dioxide. If desired, a non-freezing and non-volatileliquid may also be supplied to improve the thermal contact between thecarbon dioxide and the bottom of the receptacle. The external surface ofthe bottom of the receptacleand a portion of 'its sides thus becomes alow temperature refrigerating surface as long as any appreciable amountof solid carbon dioxide is maintained within the receptacle. Therefrigerating surface is included in an air-tight container of which thereceptacle forms a part, this container being adapted to enclose asuitable substance having desirable melting and boiling points such asto permit it to exist in a liquid phase at a suitably low temperature torefrigerate a cabinet of given dimensions and insulation. The containerholding this secondary refrigerant is preferably sealed so as to beair-tight after substantially all the air has been exhausted therefrom.The secondary refrigerant may be a substance such as, for example,carbon tetrachloride, this substance having a meltingpoint at about 11below zero F. During the operation of the apparatus, the relatively lowtemperatures within the gasholding container result in a comparativelylow pressure of the gas or vapor therein, hence the container acts as asort of vacuum flask about the-solid carbon dioxide to minimizeundesired access of heat to the sides of the inner receptacle for thesolid carbon dioxide. The container surrounding the receptacle ispreferably of sufficient size to hold a considerable quantity of liquidcarbon tetrachloride or other secondary refrigerant. This substance iskept at a desirably low temperature by evaporation of a portion of theliquid, this evaporation being facilitated by the comparatively 'lowpressure maintained within the receptacle. 1

In starting the operation of the refrigerator, the vapor in thereceptacle at first condenses in considerable quantity on the coldbottom and sides of the solid carbon dioxide receptacle, the

temperature of the bottom of this receptacle being sufficiently cold toform a frost or layer of solid carbon tetrachloride. As the vapor iscondensed on the cold surface of the receptacle in the form of frost,the pressure within the container is thus materially reduced. Undercertain conditions this reduction may be sufficient to cause anebullition of the liquid carbon tetrachloride. In any event thereduction of vapor pressure within the container by the withdrawal ofvapor to form the frost layer accelerates evaporation of the liquid.This results in a rapid removal of latent heat of vaporization from theliquid body together with resultant cooling of the liquid and of itscontainer. By this reduction of temperature, the container itselfbecomes the cold body within the refrigerator cabinet and exposed to theair within the cabinet, so that the cabinet is cooled thereby. The meantemperature of the air within the cabinet which is reached when thesystem. is in a condition of equilibrium will depend on various factorssuch as the atmospheric temperature, the efficiency of the insulation ofthe cabinet, the size of the cabinet, and the size of the coldcontainer.If the bottom of the solid carbon dioxide receptacle is of sufficientarea, the liquid carbon tetrachloride may be maintained wholly or-partlyin solid form by the rapidity of evaporation and the consequent removalof latent heat of vaporization.

0 Thus the container, in which is the secondary refrigerant for therefrigerator cabinet, may, under ature approximately 11 degrees belowzero F. It is desirable, however, to proportion the variousrefrigerating surfaces in such a manner that it will not be necessary touse the minimum temperature of the carbon tetrachloride except wheninitially cooling the cabinet.

The temperature of the secondary refrigerant maybe controlled by thefrost layer of solid carbon tetrachloride formed on the. cold surface ofthe solid carbon dioxide receptacle. This frost is a relatively poorconductor of heat so that a fairly steep temperature gradient isestablished therethrough, the thick coating of frost presenting to thegas within the container a surface temperature considerably above thatof the solid carbon dioxide. This materially retards condensation ofvapor in the vicinity of the frost layer,

,' this retardation of condensation resulting in a similar retardationof evaporation from the liquid body. This is automatically variable toadjust itself to temperature conditions within the cabinet. If, forexample, a cabinet door is opened after the system has reachedasubstantial equilibrium, the inflow of warm air from the outsideatmosphere raises the mean temperature of the cabinet. This additionalheat is absorbed by the surface of the container. the rise intemperature resulting in an increase of evaporation of liquid and anincrease of vapor pressure within the con-- tainer. A rise of pressureand temperature of the vapor tends to diminish the thickness of thefrost layer on the surface of the solid carbondioxide receptacle so thata colder surface is presented by reason of the thinner frost layerseparating the solid carbon dioxide fromthe gas. This results in anincreased rate of condensation of vapor on the frost surface whichspeedily restores the frost layer to its normal equilibrium thickness,unless the additional supply of heat from the outside is kept up. of theair originally in the container is withdrawn Since practically alltherefrom prior to the sealing thereof the motion of vapor in thecontainer is substantially unhindered, and vapor one point is almostinstantly replaced by more vapor. Apparatus of this kind may thus bemade sensitive and quickly responsive to changes of temperature withinthe cabinet so that after a door is opened for a period and then closedthe mean temperature of the cabinet is quickly reclosed vesselsurrounding the cold surfaces of'thesolid carbon dioxide receptacle, thesystem being maintained air-tight and at a very low pressure. Changes ofvapor pressure within-the vessel containing the liquid body will bequickly communicated for some distance through the connecting tube tothe-container surrounding the refrigerant. Thus the ref-rigeratingefiect is rapidly and efficiently transferred by molecular motion of thevapor.

While the mean temperature of the refrigerremoved by condensation atatorcabinet can be controlled to some extent by the relative areas of coldsurface on the solid carbon dioxide receptacle and the free surface ofthe liquid body as well as by the actual size of these areas and theprovision of efficient means for conducting heat within the cabinet tothe secondary refrigerant, I may also vary the range of temperatureswithin the cabinet by the selection of different substances or mixturesof substances having desired characteristics of melting point, boilingpoint and volatility. If, for example, a refrigerating unit of a givensize fails to maintain a certain refrigerator cabinet at a sufficientlylow temperature when carbon tetrachloride is used within therefrigerator unit, I may use a mixture of carbon tetrachloride andchloroform, or another substance such as orthochlorotoluene. Thesesubstances having lower melting points than carbon tetrachloride areeffective in establishing a lower'range of temperatures within a givencabinet, since the minimum temperature of the secondary cooling surfaceis thus made lower.

An embodiment of the invention is disclosed in the description whichfollows and on the drawing.

of Which,

Figure 1 is a side elevation of a motor truck having a refrigerator bodyincluding a refrigerating unit embodying the invention.

Figure 2 is a fragmentary section on the line 2-2 of Figure 1.

Figure 3 is a section on the line 3-3 of Figure 2.

Figure 4 is a perspective view of the refrigerating unit illustrated inthe other figures.

Figure 5 illustrates a modified form of apparatus embodying theinvention.

Referring to the drawing in detail, represents a refrigerator cabinetwhich may, as shown,be mounted on a truck chassis for the transportationof perishable foodstuffs and the like, or may be a stationaryrefrigerator for any of the purposes for which refrigerators areordinarily intended. As shown, the cabinet is provided with one or moreside doors 11 to permit the insertion and removal of merchandise whichis to be kept cool. The refrigerator unit, a perspective view of whichis shown in Figure 4, may comprise a receptacle 12 for solid carbondioxide, this receptacle being nested in a container 13 the side wallsof which are spaced from the side walls of the receptacle 12 so as toform a chamber entirely surrounding the sides of the receptacle. Thecontainer 13 is also provided with a bottom member which is likewisespaced from the bottom of the receptacle 12. The container 13 may thusbe described as a gas-tight hollow body with a re-entrant portionforming the receptacle 12 for the refrigerant. As shown in Figure 4 thecontainer may be provided with extensions 14 and 15 to receive theliquid which is to be used as a secondary refrigerant. This makespossible a relatively large free surface for the liquid body so thatevaporation thereof is facilitated. At one end of the container 13 is apipe 16 through which the liquid may be introduced into the container,and through which also the air in the container may thereafter beexhausted by a suitable pump, whereupon the pipe 16 is sealed off. Inorder to increase the effectiveness of the secondary refrigerant, anumber of metal channels 17, or other equivalent fins, may be welded,brazed or otherwise mounted on the bottom of the container 13 inintimate contact therewith. These channels preferably extend from oneside-of the cabinet to the other, or from one end of the cabinet to theother, according to the arrangement of the channels therein. Since anormally low pressure is maintained within the container 13, I mayprovide a number of supporting studs or pins 18 and 19 within thecontainer to prevent collapse of the walls thereof. The studs 18, 19 maybe spot welded to the bottom plate of the container 13, the upper endsof the studs 18 resting against the upper plates of the extensions 14and 15, the upper ends of the studs 19 restingagainst the bottom of thesolid carbon dioxide receptacle 12.

. As shown in Figure 2, the receptacle 12 may be provided with a numberof fins 20 (not shown in Figure 4) in intimate contact with the innersurface of the bottom thereof. The solid carbon dioxide, a block ofwhich is illustrated at 21, rests on the fins 20 when inserted in thereceptacle, the fins thereupon working their way up into the block sothat when the block is reduced to small dimensions the fins eventuallycut the remainder of the block into small pieces and maintain itsefficiency as a primary refrigerant until it is substantially gone.

On the bottom and a portion of the sides of the receptacle 12, a frostlayer 22 is indicated, this frost layer acting as a partial insulatinglayer and thermal valve by which the condensation of vapor within thecontainer and the resultant evaporation of more vapor from the liquidbody 23 is accelerated or retarded according to the thickness of thefrost layer. The container 13 with the channels 1'! is preferablyarranged at the top of the interior space within the cabinet, so thatthe air in the cabinet which is warmed by heat entering through thewalls or through the doors will rise andgive up its heat to thesecondary refrigerant, this resulting in more rapid evaporation of aportion of the liquid 23 and a rise of temperature within the container,with a resultant reduction of thickness of the frost layer 22. Thereceptacle 12, as shown in Figure 4, is preferably open at its top. Inorder to protect the refrigerant placed therein a well insulated coveror lid 24 may be provided, this cover being adapted to rest on suitablegaskets 25 and 26 which efliciently insulate the top of the receptacle12. Thus additional refrigerant may be supplied to the receptacle byrtemloving the lid 24 without opening the cabinet 1 se A modified formof apparatus embodying the invention is illustrated in Figure 5. Thereinis shown in section a suitable refrigerator cabinet having insulatingwalls 2'7. Within the cabinet I may place a number of containers which,as shown, may be in the form of double walled cylinders 28 of a suitablesize to receive ice-cream cans or the like, the ends of the inner andouter walls of the cylinders 23 being sealed to close the container.This container may be connected near its top to a pipe 29 leading to acontainer 30. The latter has a reentrant portion 31 serving as areceptacle for solid carbon dioxide or equivalent refrigerant. To thebottom of the container is attached a pipe 32, this pipe being connectedto a return pipe 33 leading into the lower portion of the cylindricalcontainer 28. On the other side of the container 30 there may be one ormore additional hollow containers, each preferably being connected tothe container 30 in the sarne manner as the cylinder 28, as, forexample, by a pipe 34 and a return pipe 35, the latter being connectedto the pipe 32. This illustrates a form of apparatus in which the liquidwhich is chilled by evaporation is remote from the container in whichthe insulating layer of frost is formed.

Due to the virtual absence of inert gas within the system, vapor fromthe liquid in the container .28 moves rapidly through the pipe 29 intothe container 30 to replace the vapor condensed therein. Such vapor ascondenses to liquid in the container 30 may return to the container 28through the return pipes 32 and 33.

The cabinet illustrated in Figure 5 is of a type suitable as adispensing cabinet for ice-cream or similar frozen foods. As shown, itincludes a permanent insulating top 36 having a number of aperturestherein which are closed by removable lids 37, these lids beingpreferably placed above each of the containers 28 and the container 30.If desired, an inner coverl38 may also be fitted over the refrigerantreceptacle 31. Cans of icecream or the like may be inserted by theremoval of one or more of the covers 3'7, the cansbeing preferably madeto fit loosely within the inner walls of the containers 28.

It is obvious that the specific form and arrangement of the parts of theapparatus illustrated on the drawing may be varied considerably withoutexceeding-the scope of the invention-defined in the following claims.

I claim:

1. The method of refrigerating a cabinet or the like with a refrigeranthaving a temperature far below that desired for the cabinet whichcomprises interposing and confining between the refrigerant and theinterior of the cabinet a liquid and its vapor with a freezing pointabove the temperature of the refrigerant, exposing said vapor to atemperature zone adjacent to said refrigerant lower than the freezingpoint of said vapor, whereby a portion of said vapor is condensed in asolid layer between the refrigerant and the uncondensed vapor, andexposing said liquid to a temperature zone substantially equivalent tothe temperature of said cabinet.

2. The method of controlling the refrigerating effect of a very lowtemperature refrigerant'on a refrigerator cabinet, which comprisesinterposing and confining between said refrigerant and the interior ofthe cabinet a volatile liquid and its vapor having a freezing pointabove the temperature of the refrigerant, maintaining said vaporsubstantially free from inert gases, exposing said vapor to a surfacechilled by said refrigerant to a temperature below said freezing pointwhereby a portion of said vapor is condensed on said surface in a solidlayer, and promoting the conduction of heat from the interior of saidcabinet to said liquid.

3. Apparatus of the class described comprising a closed container havinga liquid-holding portion and another portion in communication therewithand adapted to be chilled by solid carbon dioxide or the like, a mixtureof chloroform and carbon-tetrachloride within said container, thecontents of said container being substantially limited to saidchloroform and carbon tetrachlorideand their vapors, the proportion ofthese substances being according to the temperature desired for theliquid-holding portion of the container.

4." The method of controlling the flow of heat along a predeterminedpath toa refrigerant from a space to be refrigerated, which comprisesmaintaining across said path a layer of an enclosed volatile substancein its solid state and a layer of said substance in its gaseous statecontiguous to said solid layer.

5. The method of controlling heat transfer to a primary refrigerant froma region refrigerated thereby, which comprises maintaining in thethermal path from said region to said refrigerant a volatile substancehaving a freezing point above the temperature of the refrigerant and aboiling point slightly below the temperature desired for therefrigerated region, and exposing said substance to ultimateheat-exchanging proximity to said refrigerant and to said region,whereby a layer of said substance in its solid state is formed adjacentto said refrigerant.

6. The method of controlling the refrigerating effect of a lowtemperature -refrigerant on a cabinet to be refrigerated, whichcomprises maintaining between said refrigerant and cabinet a volatileheat-transferring substance simultaneously in'its three physical states,to wit, solid, liquid and vapor. I

WILLIAM F. BAIRD. 1 0

